X-ray CT (Computed Tomography) systems are a type of equipment that provides imaging of the interior of a subject by scanning the subject with X-rays for data acquisition and then by processing the acquired data with a computer.
An X-ray CT system comprises a revolving module of an X-ray tube and an X-ray detector, which are mounted facing each other on a circular ring-like frame, and the scanning of a subject positioned inside the frame is performed, with the revolving module being rotated, by radiating X-rays from the X-ray tube and by detecting X-rays that have passed through the subject with the X-ray detector.
Among scanning methods performed by X-ray CT systems, there is a scanning method called “step and shoot”. This method obtains an image that covers a broad range of the subject by the following steps: at first, a part of the subject is irradiated with X-rays and scanned into an image; then the X-ray radiation is stopped momentarily, and without X-ray irradiation, the subject together with the bed is moved by a predetermined distance in the rostrocaudal direction; then another part of the subject is irradiated with X-rays and scanned into an image; and with the cycle of translation and scanning having been repeated, the images of all the scanned parts of the subject are combined into a whole. Generally, the images of the scanned parts of the subject have some areas that overlap one another, and the overlapped areas in image are rendered with feathering. Feathering is a process that makes changes in pixel values moderate near the boundaries between the overlapped areas and the other parts of the images, which are overlapping each other.